1. Field of the Invention
The present invention relates to a sheet feeding apparatus for feeding a sheet material (for example, a transfer member) used with an image forming system such as a copying machine, printer and the like.
2. Related Background Art
The image forming system to which the present invention is applicable may be an electrophotographic copying machine, a laser beam printer, a printer using a liquid crystal shutter or an LED array, and the like.
Among these image forming systems, the laser beam printer using a laser beam (referred to as "L.B.P." hereinafter) has recently been progressed remarkably, since it provides a good image with high quality and less noise in its operation. Also in the market, the L.B.P. has been required to have a more improved function and more multiple functions. The present invention aims to provide an image forming system having an improved sheet feeding apparatus which meets one of the requirements, i.e., can solve a problem arisen when a plurality of cassette accommodating means is arranged in the system.
FIG. 9 is a sectional view of a conventional L.B.P. (laser beam printer) having a single cassette accommodating means.
This L.B.P. improves the sheet holding feature and sheet feeding ability by feeding a sheet in a substantially vertical sheet feeding path and by shortening the sheet feeding path. With this arrangement, the jamming of the sheet can be reduced and the sheet feeding ability and the reliability of operation can also be improved, since the sheet feeding direction is not varied abruptly. Further, in this L.B.P, as a whole, mechanical parts such as driving elements are arranged in the left side (FIG. 9) of the L.B.P, and electrical and optical parts are arranged in the right side of the L.B.P. With this arrangement, the treatment of the jammed sheet and the maintenance can be easily performed, and the size and the cost of the printer can also be reduced.
The construction and operation of the L.B.P will now be explained with reference to the example shown in FIG. 1.
In FIG. 9, a frame 1 of the printer includes a stationary part 1A and a rockable part 1B which can be opened to expose a sheet feeding path for a sheet S. The rockable part 1B is supported for pivotal movement around a pivot pin 2. The sheets S are accommodated in a cassette 3 acting as a sheet accommodating means and are fed out from the cassette 2 by means of a sheet supply roller 4. When, the sheet supply roller is rotated, the sheets S are separated one by one by means of the sheet supply roller and a separating pad 4 made of high friction material and urged against the sheet supply roller 4.
The separated sheet S is fed to a pair of registering rollers 7 along a pair of guides 6, and then is passed in front of an image bearing member 8 in synchronous with an image formed on the image bearing member. Thereafter, the sheet is transported to a transfer station along a transfer guide 25. The transfer station includes the image bearing member 8 and a transfer roller 9 urged against the image bearing member. The image on the image bearing member 8 is transferred onto the sheet S in the transfer station, and then, the sheet is fed to a fixing device 10.
The fixing device 10 comprises a heater roller 11 including a heater therein, a pressure roller 12 for urging the sheet S against the heater roller 11, a guide 13 for introducing the sheet S into a nip between the heater roller 11 and the pressure roller 12, a casing 14, and a separating pawl or claw 15. After the image has been fixed to the sheet S by means of the fixing device 10, the sheet S is ejected through an ejection opening 1C and collected in a tray 16. Further, by changing over a flapper 17 arranged between the fixing device 10 and the ejection opening 1C, the sheet feeding direction can be changed, whereby the sheet can be ejected through an ejection opening 1D. Incidentally, in this case, the surface of the sheet on which the image is formed is turned to the upside.
Next, an image forming station will be explained. The image forming station can perform a well-known Carlson processes and includes a process cartridge 18 enclosing various elements for executing the processes, and a scanner 19 for scanning the image bearing member 8 axially with a laser beam.
The process cartridge 18 will be explained with more detail. The image bearing member 8 is charged uniformly a charger roller 20, and a latent image is formed on the image bearing member by a laser beam L emitted from the scanner 19. Toner t in a developing container 21 is supplied to a developing station 23 by an agitating plate 22 and is coated on a developing sleeve 24 to form a thin toner layer. The toner is sticked or adhered to the image bearing member 8 in accordance with the image formed thereon to develop the image. This toner image is then sent to the transfer station mentioned above.
Next, the cassette 3 acting as the sheet accommodating means will be explained. The cassette 3 is arranged in a lower portion of the printer. If a plurality of cassettes are used, the cassettes are arranged in a overlapped condition. A direction to which the cassette is loaded or unloaded to replenish the sheets may coincide with a direction A in consideration of the fact that the sheet feeding path can be easily maintained and a mechanism for retracting the separating means 4, 5 can be conveniently provided when the plurality of cassettes are arranged in the overlapped condition. However, in this case, there arise problems that operations to be performed by an operator are more complicated and troublesome and that an installation space for the printer is considerably increased. That is to say, the operator must perform the jam treatment, exchange of the process cartridge 18 and manipulation of an operation panel in a direction Y (FIG. 9), whereas he must load or unload the cassette in the opposite direction A, and, accordingly, the operator must move to the opposite sides of the printer for performing these operations. In particular, the operator must move to the rear side of the printer whenever he performs the mainpulation regarding the cassette, which is to be most frequently performed. Further, since a space used for loading and unloading the cassette must be maintained in the rear side of the printer, the large installation space for the printer is required.
Incidentally, the Japanese Patent Laid-Open No. 59-4534 discloses a sheet feeding apparatus in which a cassette can be loaded and unloaded in a direction same as a sheet feed-out direction. However, this patent specification does not disclose the treatment of the cassette if a plurality of cassettes are used.